In recent years, in motorcycle structural parts or the like required to have a certain strength, aluminum alloy forged products have been widely used to trim the weight.
It is well known that motorcycle parts or the like have been produced by subjecting an extrude article made of, e.g., a JIS 2014 alloy, to forging. In the case of an ordinary JIS 2014 alloy extruded article, coarse recrystallization occurs at the step of heat treatment called T6 (T6 heat treatment) performed after forging, and the subsequent acid cleaning causes appearance of macro patters on the product surface. To solve this problem, as shown in the following Patent Document 1, in the case of parts used at portions which readily attract public attention, surface treatment, such as, e.g., shotblasting, is performed after the acid cleaning.    [Patent Document 1] Japanese Unexamined Laid-open Patent Application Publication H06-240420 (see claims and FIG. 1)